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broux2

Rear Main Seal

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broux2

Has anyone here ever replaces a rear main seal on a mercruiser 5.7L comp ski engine? I am trying to decide if this is something I can do myself. I appreciate any feedback.

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martinarcher

Has anyone here ever replaces a rear main seal on a mercruiser 5.7L comp ski engine? I am trying to decide if this is something I can do myself. I appreciate any feedback.

You talking about the rear tranny seal? I've replaced it myself. It's not too bad. Took a couple afternoons. If I remember right the seal was around $6.

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broux2

You talking about the rear tranny seal? I've replaced it myself. It's not too bad. Took a couple afternoons. If I remember right the seal was around $6.

I do not think is is a tranny seal. It is the seal in the back of the engine where the flywheel is. The seal is the what holds the engine oil from leaking out the back. I think I can do it but i just need to know ig the engine has to come out. If the oil pan does not need to be dropped i think I am all set.

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nevertwobig

Hi there, Are you sure its the rear main? It could be the oil pan gasket where it meets the bearing housing. I had a 91 I/O with a 5.7 and I pulled the motor and took off the bell housing and the flywheel and seal was bone dry. The gasket on the oil pan was leaking where it met the bearing housing. Also thought I had a main leak on a 2001 moomba with a 5.7. Turns out the boat sat for a year and the seal just dried out, the previous owner also used synthetic oil which is a thinner oil. Went back to regular 15W-40 oil and problem went away. Hope this helps!

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martinarcher

I do not think is is a tranny seal. It is the seal in the back of the engine where the flywheel is. The seal is the what holds the engine oil from leaking out the back. I think I can do it but i just need to know ig the engine has to come out. If the oil pan does not need to be dropped i think I am all set.

OK. Yeah the seal I changed is where the drive shaft exits the Velvet Drive Transmission. It doesn't hold any motor oil in, just tranny fluid.

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Woodski

A couple of things to investigate before digging in. You could have some of the suspect oil checked for chemical content to identify if trans or motor oil. First, does it leak/seep/drip while the boat has been sitting for a long time or after running the boat you find oil in the bilge. If the latter, is there oil windage on the backside of the flywheel, that would support the rear main suggestion. If the former, could there have been too much oil in the crankcase which ended up seeping out due to sitting?

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tvano

my 5.7L was leaking oil from the nipples and tee that feed the oil sending units.

the migration path was not evident and it ended up looking like the rear main engine oil seal was leaking.

check it out closely; it is a much easier task to fix than pulling the transmission to peek at the rear main.

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broux2

The leak is coming from multiple places in the bell housing. It does not appear to happen while sitting, only running. The places it leaks are a small hole near the oil filter as well as a cover on the bell housing. I opened the rubber seal on top of the bell housing to see the flywheel and everything is covered in oil. I am pretty sure the rear main is leaking. I talked to a mechanic i know and he said if it is a one pice it is easy. If it is two the whole engine has to come out. Look at the diagrams for parts it appears to be a one piece. Looks like I am gonna give it a try. Any good suggestion on supporting the motor when i remove the tranny?

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tvano

The leak is coming from multiple places in the bell housing. It does not appear to happen while sitting, only running. The places it leaks are a small hole near the oil filter as well as a cover on the bell housing. I opened the rubber seal on top of the bell housing to see the flywheel and everything is covered in oil. I am pretty sure the rear main is leaking. I talked to a mechanic i know and he said if it is a one pice it is easy. If it is two the whole engine has to come out. Look at the diagrams for parts it appears to be a one piece. Looks like I am gonna give it a try. Any good suggestion on supporting the motor when i remove the tranny?

iirc you will need to remove some odds n ends hoses, fuel lines, shift cables, etc..

pull the bolts from the drive shaft coupling.

loosen the front engine mounts, block the rear of the transmission and remove the rear engine mounts.

removing the rear mounts is easier if you slide the engine to one side while working the engine mount on the other side.

iirc a 3/8" hex bit socket is helpful. i think i pulled the hex bit out of the socket (it was pinned w a tiny socket head screw) and used a 3/8" box end for leverage.

once the rear mounts are off you will be able to pivot the engine around the front engine mount (rear of the engine up as the front dips).

i rigged up a nylon tow strap from the transmission tail-stock up to a hydraulic floor jack that was positioned on 4x4 blocks.

it covered most of the lifting chore pretty swell.

after swinging the rear of the engine up i blocked it so i could remove the floor jack and get some elbow room.

i pulled the bell-housing and transmission as one piece.

the transmission is heavy/bulky, ungainly. another set of hands may be helpful, sometimes.

remember to pull and clean the screen from the bottom of the transmission as long as the transmission is rolling around the garage floor.

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martinarcher

I used a 6X6 spanning 4 of my rafters in the garage to hold the rear of my motor with a come-a-long and a couple good nylon tow straps. Don't forget to disconnect the exhaust too.

Edited by martinarcher

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broux2

I was able to lift the back of the engine but where do I put blocks to hold it up. Is is all oil pan under there and i am a little nervous about it holding the weight of the engine. Any ideas?

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Woodski

I would try to set the engine on blocks that rest it on the oil pan rails, that should be the easiest and will have plenty of strength. In reality the pan should hold it, but I certainly understand your concern and certainly the rails will be fine.

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broux2

Thanks for all the help. I have successfully changed the seal. Luckily it was a one piece seal. I ended up building a tall saw horse and was able to use a come-along to raise the back of the engine. I never blocked the engine as it was supported very well with that setup. I did end of having to drop the oil pan as I could not get the new main seal past the oil pan seal. Time to finally put her back in the water.

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